1. Field of the Invention
The invention relates, in general, to devices for joining strips of material together and, in particular, to a new and useful device for welding plastic foil strips together as they are fed into juxtaposition with overlapping edges.
U.S. Pat. No. 4,146,419 shows a device for the welding of plastic foils overlapping at their edges. It includes a heating edge for the heating of the overlapping foil edges, a front pair of pressure rolls and a rear pair of pressure rolls. The upper pressure roll of each pressure roll pair are each mounted on an angle lever. A pressure spring arranged between the angle levers, which are adjustable by turning a set screw, presses the upper pressure rolls against the lower pressure rolls, thus creating the pressure necessary for the welding of the softened foil edges.
A major disadvantage of this device is that when new foils are inserted between the pressure roll pairs, the angle levers have to be moved manually against the tension of the pressure spring to open a gap sufficiently wide for the insertion of the foils between the upper and the lower pressure rolls. The welding pressure is comparably high for strong foils and therefore the required force has to be high. The operator has to exercise relatively strong force to move the angle lever. The force required is even increased by the fact that angle levers have to be moved further for the insertion of strong foil than for thin foil.